Lithium alloys are used as the active anode material in thermal batteries, of both the primary (non-rechargeable) and the secondary (rechargeable) types. Such cells are activated for operation by heating to a temperature above about 400.degree. C., in order to melt the otherwise solid electrolyte. Typically the electrolyte is a mixture of alkali metal halides, for example a eutectic mixture of potassium chloride and lithium chloride which melts at about 350.degree. C. Common cathode materials, among others, are iron pyrite, calcium chromate and copper oxide. Pure lithium metal can be used as the anode in such cells, but it is very low melting (180.degree. C.) and would be molten at the temperature at which the electrolyte melts, so that it might spill or flow within the cell, with resultant failure.